Generally drawn are stud welding utilizes stud welding devices that are powered by a three phase 480 volt line power. Such power supplies utilize a three phase industrial power requiring a qualified electrician to connect and disconnect and often requiring crane or forklift operators to relocate them. Additionally, three phase power drops may not be readily available at fabrication shops and repair sites and studs are often welded with inefficient stick welding (SMAW) power sources using available single phase power. Capacitor discharge (CD) stud welding is often powered by domestic single phase supply but CD is restricted to small diameter studs and is not as reliable as drawn-arc stud welding.
There is therefore a need in the art for a drawn arc stud welding power supply that may utilize a single phase domestic line power such as a 115 volt AC in the U.S. or a 230 volt AC in Europe.
There is also a need in the art for a drawn arc stud welder that reduces the input voltage necessary for a drawn arc welding operation. A lower voltage power supply will allow for use in locations where a 3 phase 480 volt or 400 volt industrial power supply is not present. Additionally, there is a need in the art for a drawn arc welding process and power supply providing high quality welds that are easy to inspect and deliver a predictable weld.
Prior art patents associated with welding operations and specifically drawn arc stud welding operations and devices fed by single phase domestic power are deficient for providing a power source in which a current may be adjustable and regulated. For example, prior art U.S. Pat. No. 7,858,895 discloses a portable drawn arc stud welder with a battery as an energy device. The patent discloses using a battery charger to charge a battery and then uses three MOSFET circuits in parallel to discharge the battery with timer controls to provide a fixed time pulse from 0.1 to 1.1 seconds in duration with current given by output circuit drop (cables, etc.) and battery impedance. However, the prior art patent includes disadvantages in that the welding current may not be adjusted and that the welding current is nonregulated.
Additionally, U.S. Pat. No. 7,183,517 discloses a portable welding-type apparatus that has an energy storage device. The '517 patent discloses a welding power source that includes an energy storage device such as a battery which supplies power to a boost converter linked with a buck converter whose output is then utilized for SMAW, GMAW, GTAW, plasma cutting, and heating. In contrast with a drawn arc stud welding process, the '517 prior art patent requires a boost converter and is configured for other types of high duty cycle welding processes where the welding power is drawn from the energy storage device continuously during welding, typically in minutes per weld. In contrast a drawn arc stud welding has a very low duty cycle, typically in a fraction of a second per weld. Additionally, a drawn arc stud welding process needs a temporary energy storage to accumulate enough energy for a stud welding operation as a typical household line power with a 20 amp service is insufficient in wattage for a typical drawn arc stud welding operation directly without energy storage ahead of welding. The topology disclosed in the '517 prior art patent is intended to utilize current from a low voltage battery continuously while welding thus requiring the boost converter to boost the voltage from the low battery voltage to a higher voltage suitable for use by the various arc welding and cutting processes.
There is therefore a need in the art for an improved drawn arc welding power supply and process that overcomes the deficiencies of the prior art.